The present application claims priority under 35 U.S.C. xc2xa7119 to Japanese Application No. JP 11-123183 filed Apr. 28, 1999.
The present invention relates to a novel mouse, in which human T cells have been engrafted, which is useful as an animal model for the in vivo analysis of the differentiation and proliferation of human T cells, functions thereof and the like, and to a method for developing the mouse. More particularly, the present invention relates to a method for developing a novel human T cell-engrafted mouse, which comprises transplanting a human-derived bone tissue into an inbred line mouse deficient in immune cells such as B cells and T cells, as well as to a novel mouse obtainable by this method, in which human T cells are present in blood at a high percentage for a long period of time. Furthermore, the present invention relates to an application of the novel mouse as an infectious model with a human immunodeficiency virus (hereinafter abbreviated as HIV).
In spite of great efforts so far made to overcome AIDS, a conclusive method for treating this infectious disease having a high morbidity and mortality has not been established. One of the serious obstacles in the studies of treatment of AIDS at animal levels is that small animals in wide use, such as mouse, are not infected with HIV. While experiments using primates, such as rhesus monkey, have been recently performed, the primates are highly expensive and cannot be used frequently for laboratory level experiments. Therefore, there is a great demand for developing a mouse model artificially treated to become susceptible to HIV infection.
A primary approach to solving the above-mentioned problem is to make HIV infectious human-derived immune cells exist within the body of a mouse. Thus, many attempts have been made to develop a mouse model having human blood cells, in particular, human T cells, by transplanting a tissue comprising these cells or a tissue capable of producing them into a mouse.
For example, J. M. McCune et al. (Science, 241(4873): 1632-1639 (1988)) transplanted fetal human tissues (thymus and liver or bone) to under renal epithelium of a C.B.-17 scid/scid mouse (hereinafter to be referred to as SCID mouse), which congenitally lacks mature B and T cells due to gene rearrangement function disorder, whereby a SCID-hu mouse was prepared, in which hemopoietic stem cells derived from the liver or bone marrow appear in the periphery via the transplanted human thymus, so that human T cells are identified in the peripheral blood. In most cases, however, the frequency of appearance of human cells in this mouse is very low. Moreover, a fetal human tissue is not readily available. Accordingly, this mouse is not predominantly used.
In contrast, an hu-PBL-SCID mouse (D. E. Mosier et al., Nature, 335(6187): 256-259 (1988)), which is prepared by intraperitoneally administering nucleated cells in human peripheral blood or peripheral blood stimulated with IL-2 to a SCID mouse, in which human T cells appear in peripheral blood, is being used in number at present as an experimental model for HIV infection, because it can be produced overwhelmingly easily as compared to the SCID-hu mouse. However, this mouse again shows low frequency of human T cell appearance. In addition, this mouse disadvantageously shows an unusual CD4+ cell/CD8+ cell ratio (hereinafter to be abbreviated as CD4/CD8 ratio) wherein CD8 positive cells are mostly dominant.
In view of the low proportion of human T cells in peripheral blood of any mouse model, T cell chimerism in blood has been improved by irradiation or administration of an anti-NK antibody (D. K. Kim et al., Eur. J. Haematol., 61(2): 93-99 (1998)).
A NOD/Shi-scid Jic (NOD/SCID) mouse, which has been recently developed (R. M. Hesselton et al., J. Infect. Dis., 172(4): 974-982 (1995)), shows lower activities of not only T cell and B cell but also other immune cells such as NK cell and macrophage, thereby allowing 5 to 10 times higher incidence of engrafting of human cells than in conventional SCID mice. Even if this mouse is used as a recipient for an hu-PBL-SCID, however, the T cells of the resulting mouse are still CD8 positive cell-dominant, which means that the mouse is insufficient as a model for HIV infection.
While there are some reports on transplantation of a bone tissue derived from a human adult into a SCID mouse (e.g., Y. Heike et al., Blood, 86(2): 524-530 (1995)), none of which succeeded in engrafting human T cells.
As mentioned above, all conventional human T cell-engrafted mice have a drawback, such as a low frequency of appearance of human T cells in blood, a failure to sustain the effect for a long time and/or a different CD4/CD8 ratio from a human, i.e., being CD8 positive cell dominant and the like. As the situation stands, there has not been found any satisfactory HIV infection model.
It is therefore an object of the present invention to provide a human T cell-engrafted mouse in which human T cells appear in blood at a high frequency for a long time and which has a CD4/CD8 ratio approximate to that of human, and a method for developing such mouse. It is a further object of the present invention to provide an HIV-infected mouse model superior to conventional ones, by infecting a human T cell-engrafted mouse model with HIV.
The present inventors have transplanted a bone tissue derived from a human adult to an inbred line mouse lacking immune cells including B cells and T cells, particularly NOD/SCID mouse, as a recipient. As a result, they have succeeded in providing a mouse, in which T cells can proliferate and which shows high T cell chimerism in blood for a long time. In addition, they have confirmed that the mouse shows significantly higher CD4/CD8 ratios in blood and each organ than those of known mouse models, and is more preferable as an HIV infection model. Furthermore, the present inventors actually infected this mouse with HIV and confirmed reduction of CD4 positive T cells after infection, demonstrating that the mouse model can be a superior HIV infection model, which resulted in the completion of the present invention.
Accordingly, the present invention provides the following.
(1) A human T cell-engrafted mouse, wherein human bone tissue-derived T cells exist in peripheral blood at least for 2 months, and, for a certain period of time during this 2 month period, a proportion of human cells in blood becomes more than 10%, preferably more than 30%.
(2) A method for developing a human T cell-engrafted mouse comprising transplanting a human-derived bone tissue into an inbred line mouse lacking immune cells inclusive of at least B cells and T cells, preferably an inbred line mouse further deficient in NK cell activity and/or macrophage activity, most preferably a NOD/SCID mouse, preferably into the extraperitoneal cavity of said recipient.
(3) The human T cell-engrafted mouse obtainable by the method of (2) above, wherein human bone tissue-derived T cells exist in peripheral blood at least for 2 months from about 1 month to about 3 months after transplantation, and, for a certain period of time during this 2 month period, a proportion of human cells in blood becomes more than 10%, preferably more than 30%.
(4) The mouse of (1) or (3) above, wherein a part of said human T cells is capable of being infected with HIV.
(5) A method for preparing an experimental HIV-infected mouse model, which comprises infecting the mouse of (4) above with HIV.
(6) An experimental HIV-infected mouse model obtainable by the method of (5) above.
According to the method of the present invention, it is possible to develop a blood-chimeric mouse in which human T cells appear in peripheral blood at a high frequency for a long time, and the inventive method is useful in in vivo analysis of differentiation/proliferation and functions of human T cells. This mouse model also serves well as a recipient of immune response induced by transplantation of tumor cells. Furthermore, since the blood-chimeric mouse prepared by the inventive method has a higher CD4/CD8 ratio than that of conventional mice, and has T cells that express both CD4 and CXCR4 markers, which are HIV receptors, it is strikingly useful as a model of HIV infection.